In the world of "As You Like It," the court symbolizes all that is corrupt, corrupting, and dangerous, and the forest is the emblem of natural goodness and freedom (even though living in the forest can be physically challenging).
That the court is corrupt we know immediately from Duke Senior's situation in which his younger brother has usurped his power and taken his lands. In fact, when Charles says that "there's no news at the court, sir, but the old news," he is affirming the fact that the court is, and has always been, a place of intrigue and danger. In order to save his own life, Duke Senior needs to get as far away from the court as he can, both physically and spiritually.
The old duke finds his safety not in another court but in the forest of Arden:
They say many young gentlemen flock to him every/day, and fleet the time carelessly, as they did in the golden world. . . .(1.1.3)
Shakespeare's reference to the "golden world" helps further the contrast between the corrupt court and the wholesome freedom of the forest because Shakespeare is reminding the audience that the Arden Forest is what remains of the golden world, an earthly paradise. The forest, according to Duke Senior, is "more free from peril than the envious court."
An important theme in Renaissance literature is that life in cities and at court has a debilitating effect on men that turns them from their natural instincts and behavior and to become corrupt and evil, no longer natural men. Although exile in the Forest of Arden has its discomforts, it also allows men to feel alive and free:
Even till I shrink with cold, I smile and say/"This is no flattery;these are counsellors/That feelingly persuade me what I am." (2.1.1)
Duke Senior, for the first time, feels alive: it doesn't matter that he's freezing in the cold wind because the elements remind him of his natural state. While living in the court, he was isolated from nature, and that isolation creates the corrupting effect of court life.
In essence, then, life at court and life in the forest are at opposite ends of a spectrum of behavior: the court breeds envy and corruption; country life, specifically, life in the wild forest, brings men closer to nature and their natural state, free of the corruption and jealousy that removed Duke Senior from his rightful station.